Water treatment process

ABSTRACT

An improved water softening process is provided which also reduces anion content. A first stream of water is passed through an anion-exchange unit to remove undesirable anions and raise the pH. The first stream of water is then provided to reactor/clarifier water softening equipment, where it acts as a source of hydroxyl ions. Preferably a second stream of water which did not pass through an anion-exchange unit is also provided to the water softening equipment. The streams of water are combined and processed through the softening equipment, where hardness ions are precipitated out, yielding softened water with reduced anion content. The anion-exchange system utilized preferably has a counter-current continuous resin train and a counter-current continuous resin regeneration unit.

This application is a division of U.S. application Ser. No. 09/099,351,filed Jun. 18, 1998, now U.S. Pat. No. 6,059,974.

This application claims the benefit of U.S. Provisional Application No.60/050,200, filed Jun. 19, 1997.

FIELD OF THE INVENTION

The invention relates generally to water treatment and more particularlyto an improved process for softening water while reducing anion content.

DESCRIPTION OF RELATED ART

Hardness in water is a common problem. Hardness in water is dueprimarily to the presence of Ca²⁺ and Mg²⁺, and also to the presence ofBa²⁺ and Sr²⁺, all of these being hardness ions. Water is said to be“softened” when these cations are removed, such as by water softeningequipment. For large-scale or large volume water softening, thetraditional process is called cold lime or cold lime-soda softening. Inthis process the lime can be either hydrated lime (Ca(OH)₂) or quicklime(CaO). In large systems the lime source is stored in a storage vessel.If quicklime is used, it must first be converted to hydrated lime(Ca(OH)₂) by being slaked, that is, combined with water. In any event,Ca(OH)₂ is provided and is diluted in a lime slurry, where the Ca(OH)₂dissociates into Ca²⁺ and 2OH⁻. This lime slurry is then fed to thereaction section of the lime softening equipment, where the OH− combineswith Mg²⁺ to form Mg(OH)₂, which precipitates out. The original Ca²⁺hardness in the water, and the Ca²⁺ introduced via dissolved lime, areremoved by a different reaction. If there is sufficient naturalbicarbonate (HCO₃ ⁻) in the water, some of the OH⁻ will react therewithto yield carbonate (Co₃ ²⁻), which will combine with the Ca²⁺ to formCaCO₃, which precipitates out. If there is insufficient naturalbicarbonate, soda ash (Na₂CO₃) is added (which converts to 2Na⁺ and CO₃²⁻) and again the CaCO₃ forms and precipitates out. (Soda ash usageunfortunately adds substantial Na⁺ to the finished water). As analternative to using Ca(OH)₂ as the source of OH⁻, sodium hydroxide(caustic soda) (NaOH) has been and is used. Sodium hydroxide also addssignificant quantities of sodium ion to the final water and removesessentially no anions other than bicarbonate.

The traditional lime process generates considerable sludge, being CaCO₃and Mg(OH)₂, and does little if anything to reduce chloride content andhas limited capability to reduce any of the other anion content(sulfate, phosphate, nitrate) of the initial water. When it is necessaryto use soda ash (due to low influent bicarbonate content), thetraditional process increases the sodium content of the final effluent.

As can be seen, the key to removing hardness is the introduction of OH⁻.The OH⁻ converts Mg²⁺ to Mg(OH)₂, and converts HCO₃ ⁻ to CO₃ ²⁻, whichthen reacts with Ca²⁺ to form CaCO₃. (If there is insufficient naturalHCO₃ ⁻, Na₂CO₃ is added). In the traditional hydrated lime treatmentprocess, the OH⁻ is supplied via Ca(OH)₂.It is also traditional to useNaOH as the OH⁻ source with the lime treatment equipment.

There is a need for an improved water softening process which eliminatesor reduces the drawbacks of the traditional lime softening process.

SUMMARY OF THE INVENTION

A process for softening water comprising the steps of

(a) passing a first stream of water through an anion-exchange unit toraise the pH of said first stream and provide a second stream of waterhaving a pH of at least 9.5;

(b) providing said second stream of water to water softening equipmentcomprising reactor and clarifier sections, said second stream of waterbeing used as a source of hydroxyl ions in said water softeningequipment;

(c) processing a fourth stream of water through said water softeningequipment, said fourth stream comprising said second stream; and

(d) operating said water softening equipment on said fourth stream ofwater to remove via precipitation reactions hardness ions from saidfourth stream and to provide thereby a fifth stream of water.

An anion-exchange system comprising a counter-current continuous resinregeneration unit is also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a water treatment process according tothe invention.

FIG. 2 is a schematic diagram of an alternate water treatment processaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

As used herein, parts are parts by weight unless otherwise indicated andparts per million (ppm) and parts per billion (ppb) are parts by weight.When a preferred range such as 5-25 is given, this means preferably atleast 5 and preferably not more than 25.

With reference to FIG. 1 the diagram includes a conventional lime/sodawater softening equipment or contact solids water treatment unit orportion or system (reactor/clarifier) which is basically operated aswater softening equipment in the conventional manner except as noted.This water softening equipment consists essentially of a first stagemixing tank or reaction zone or section 20, an optional second stagemixing tank or reaction zone or section 21 and a clarifier or clarifiersection 33 having a flocculation zone 35 and a settling zone 36.

Other conventional cold or hot process lime or lime/soda water softeningequipment or contact solids reactor/clarifier can be used. Influentwater (typically pH 6-8 or about 7) to be treated comes in via line 23at a flow rate of preferably 20-5000, more preferably 50-1000, morepreferably 100-800, optionally 200-600, gallons per minute; some or all(preferably 10-100%, more preferably 25-50%, more preferably 30-40%,more preferably about 33%) of the influent water passes through line 30to the anion-exchange unit 38 for anion-exchange and the remainder ofthe influent water passes through line 32 directly to mixing tank 20,lines 30 and 32 each being portions of line 23. This is preferablycontrolled by pH controller 25 or similar device sensing tank 20 andcontrolling valves 43 and/or 44. Preferably pH controller 25 senses thepH of tank 20 and controls the valves 43 and/or 44 so as to maintain thepH of tank 20 at a pH of at least 9.5, more preferably at least 9.8,more preferably at least 10, more preferably at least 10.3, morepreferably at least 10.6, more preferably at least 10.9, optionally atleast 11.3. The pH of tank 20 is preferably 10-12.5, more preferably10.3-12, more is preferably 10.3-11.6, more preferably 10.6-11.2. Thepreferred method is to control the flow through line 32; less preferredis to control the flow of water through line 30. If all the influentwater is diverted through the anion-exchange unit, this usually resultsin the water in tank 20 being too caustic; however, in some situationsall the influent water can go through the anion-exchange unit, so the pHof the effluent from the anion-exchange unit is the pH of the water intank 20. The preferred maximum pH of the effluent from theanion-exchange unit is 13.3 or, more preferably, 13.

The influent water is preferably at ambient temperature and ispreferably neither heated nor chilled during the process. Sometimes theinfluent water may be above or below ambient, such as hot influent waterreceived from a cooling tower.

The traditional ion exchange unit has two parts, the cation unit and theanion unit. In most installations the water first goes into a cationunit, where the cations including Ca²⁺ and Mg²⁺ sorb to the resin,releasing H⁺. The water then goes to the anion unit, where the anions(sulfate SO₄ ²⁻, nitrate NO₃ ⁻, phosphate PO₄ ³⁻, chloride Cl⁻, silicateSiO₄ ⁴⁻, etc.) sorb onto the resin, releasing OH⁻. Then the H⁺ and OH⁻combine to yield ion-free, or deionized, water.

In the present invention only the second of these two units, the anionunit, is used. The anion unit basically takes the naturally occurringanions (sulfate, nitrate, chloride, etc.) out of the water and producesa caustic, alkaline solution high in OH⁻. This alkaline, high pHsolution is then used in the treatment equipment as a source of OH⁻ andthus eliminating the need for either Ca(OH)₂ or NaOH.

Anion-exchange system 22 is shown having an anion-exchange unit 38 whichin this embodiment is counter-current continuous anion-exchange resintrain 38 (comprising first stage tank 40, second stage tank 41 and thirdstage tank 42), and a counter-current continuous resin regeneration unit39 having first stage tank 50, second stage tank 51, third stage tank52, fourth stage tank 53 and fifth stage tank 54. Anion-exchange unit 38and regeneration unit 39 are operated as fluidized beds. Anion-exchangeunit or resin train 38 is shown having three conebottom tanks 40-42; itmay optionally have 2-6 or more preferably 3-5 tanks. Each such tank isfilled preferably to 20% to 40% of capacity with anion-exchange resin,preferably in bead form as is known in the art. There is a sufficientnumber of tanks in the train 38 and each tank is of sufficient size sothat the total contact time of the water with the resin beads ispreferably 10-30, more preferably 15-25, minutes, so as to permiteffective anion exchange on the resin. Thus if the flow rate through theresin train 38 is 100 gallons per minute and there are three tanks each40% filled with resin beads, each tank may preferably be 1667 gallons.Influent water travels through the tanks 40-42 through line 30, thenline 30 a, then line 30 b, then exiting through line 24.

Typically there are 5-7 tanks in regeneration unit 39, each typicallyabout half the size of the tanks in train 38. Regeneration unit 39 isrun so that the resin beads are regenerated at about the same rate orspeed as they are used up in train 38. The resin beads go through theresin train 38 via the pathway of line 45, then line 45 a, then line 45b. To be regenerated, the resin beads follow the pathway of line 56 thenlines 57, 58, 59, 60, and 61 to storage tank 62. The rinse water(preferably from tank 42) goes through lines 63, 64 and 65 to tank 52.Regenerant solution (preferably 50% NaOH) goes through line 66 into tank52 where it joins the rinse water to form a typical 4% NaOH brine, thenthrough lines 67, 68 and 69 to spent regenerant tank 70. Spentregenerant is preferably collected into a separate clarifier wherecalcium sulfate, calcium carbonate, magnesium hydroxide and otherprecipitants and suspended solids that are flushed from the regeneratingresin are collected.

The preferred counter-current design does not require the installationof a pre-filter as the counter-current principal continuously flushesthe resin and suspended solids are washed away. In addition, thecounter-current design does not require a backwash step prior to theregeneration of the anion resin. This method also uses far less resinand has a lower resin 17 capitol cost. Compared with the batch system,the resin is also less stressed with less cracking and breakage andregeneration 19 rates are far higher yielding better regenerant usageand lower regenerant cost. The continuous counter-current design alsouses water from the process (such as from tank 42) as resin rinse waterand regenerant dilution water. The spent regenerant from thecounter-current process will be a high solids salt solution such asNaCl, Na₂SO₄, NaNO₃, Na₃PO₄, Na₂HPO₄, etc. that is suitable for otheruses. The concentration of this spent stream can be in the range of 4 to7% depending on process design.

Less preferably counter-current continuous resin train 38 and/orcounter-current continuous resin regeneration unit 39 can be a batch orsingle-tank process or system or setup using comparably or appropriatelysized tanks as known in the art. Batch regeneration has the resincollected in a batch tank and then regenerated with regenerant solution.The regenerated resin is fed to a storage tank to supply regeneratedresin to the head of the process train. Spent regenerant is allowed tosettle in a storage tank where solids are separated off.

The anion-exchange resin is preferably a crosslinked polystyrene matrix,strongly basic anion-exchange resin, gel type (Type II), in bead form,preferably DIAION SA 20A from Mitsubishi Chemical, which are 0.4-0.6 mmdiameter beads having a total capacity (Meq/ml)(Min.) of 1.3. OtherDIAION anion-exchange resin beads from Mitsubishi Chemical can be used,including DIAION PA 408 and PA 418, which are porous type (Type II)having total capacity (Meq/ml)(Min.) of 0.9-1.3. Less preferredanion-exchange resin beads include Rohm and Haas Amberlite IRA-410, astrongly basic, Type II, quaternary ammonium anion-exchange resin, andweakly basic anion-exchange resins made of crosslinked polymethacrylateand crosslinked polyacrylate, and Type I anion-exchange resins. Usefulanion-exchange resin beads may also be obtained from Dow Chemical,Purolite, Mobay, and other sources as known in the art.

In the anion-exchange unit 38 anions such as Cl⁻, SO₄ ²⁻, NO₃ ⁻ andother anions (phosphate, silicate, etc.) are removed and are replaced byOH⁻ ions, thus raising the pH and becoming a caustic solution. Thetreated water leaving the anion-exchange unit 38 via line 24 has a pH ofpreferably 9.5-13.3 as described above, more preferably 12-12.8, morepreferably about 12.3-12.5. The water from line 24 combines withuntreated water from line 32 and goes into mixing tank 20.

Mixing tank 20 is sized as a function of the flow rate to providepreferably 10-30, more preferably about 15, minutes of contact time.Thus a flow rate of 10 gallons per minute with 15 minutes contact timewould require a 150 gallon tank. In tank 20 OH⁻ combines with Mg²⁺ toyield Mg(OH)₂ precipitate. (Silicate is co-precipitated in thisprocess). The OH⁻ also combines with naturally occurring HCO₃ ⁻ to yieldCO₃ ²⁻, which combines with Ca²⁺ to form CaCO₃ precipitate. In tank 20there is precipitated primarily Mg(OH)₂ and as much CaCO₃ as the naturalHCO₃ ⁻ alkalinity will permit. If there is sufficient natural HCO₃ ⁻carbonate alkalinity, then mixing tank 21 is not needed.

Optional mixing tank 21 is the same size as tank 20. If naturalbicarbonate alkalinity is low or insufficient, carbon dioxide can be fedor injected via line 26 into mixing tank 21 to force the precipitationof calcium as calcium carbonate. (CO₂+2OH⁻→H₂O+CO₃ ²⁻; CO₃²⁻+Ca²⁺→CaCO₃). This can be controlled by a calcium hardness analyzer ora pH controller (not shown) sensing tank 21, where the pH is preferably9.5-11.5, more preferably 10-11, more preferably 10.3-10.7. As has beendescribed and as is shown in FIGS. 1 and 2, the water softeningequipment is operated on the stream of water to remove via precipitationreactions hardness ions from the water to yield or provide a stream ofwater having reduced hardness and reduced anion content.

The effluent from tank 20 (or tank 21 if it is used) goes to clarifier33 for flocculation, settling and clarification as known in the art.Clarifier 33 is sized as a function of flow rate and rise rate, as knownin the art. Sludge is pumped via line 28 to a filter press or somesimilar dewatering device. Treated effluent water passes via line 29 toa process use or other end use or reuse as effectively softened water;it may optionally be neutralized to a lower controlled pH by addition ofcarbon dioxide via pH controller 34. Less preferably mineral acid can beused to lower the pH. If sent to a sewer or as process water, the pH ispreferably 6-9; if sent for cooling water, the pH is typically 6 or 7 to8.5.

Optionally a second clarifier can be provided between first stage mixingtank 20 and second stage mixing tank 21. In this configuration, highrates of magnesium and silica removal are achieved. The sludge from thisintermediate clarifier will have commercial value for its magnesiumhydroxide content (if the influent is not highly contaminated). Theeffluent from this intermediate clarifier is then passed into the secondstage mixing tank where optional carbon dioxide is added and calciumcarbonate is precipitated. This two-stage process has very highmagnesium and calcium removal rates. The magnesium can be dropped tounder 1 ppm with calcium reduced to under 10 ppm while sulfate can bereduce to under 50 ppm. Chloride reduction becomes a function of thecounter-current stages used in the design or the recycle rate throughthe unit.

Similarly to FIG. 1, the invention can less preferably be practiced in asituation where the mixing tanks and clarifier are replaced by a linedor encased pond (such as a wastewater pond or environmental pond) orsimilar tankage. In such situations the ponds or tankage would havereactor and clarifier sections.

Alternatively, tank 20 can receive (a) effluent water from two or moreseparate or independent anion-exchange units and (b) untreated water(ie, water which has not gone through an anion-exchange unit) from oneor two or more sources separate or independent of or in substitution forinfluent line 23 and/or line 32, such as a series of wells or a seriesof process lines to be softened for reuse. For example, line 30 could befrom a first well and line 32 could be from a separate, second well.

FIG. 2 illustrates a less preferred water treatment system according tothe invention. It is in most ways the same as FIG. 1. In FIG. 2 thethick line shows the principal flow of water. Line 1 carries alkalinesolution (high in OH⁻) as anion unit effluent (pH preferably 11-13.1,more preferably 12.3-12.7) from the anion-exchange unit 10 to the firststage mixing tank or reaction zone 2. Mixing tank 2 also receivesuntreated influent water via line 13. The water then flows throughoptional second stage mixing tank or reaction zone 3, clarifier 5, andinto line 7 via pump 6. A portion (typically less than half) of thewater from line 7 (having pH of preferably 9.5-13.1, more preferably10.3-10.7) is carried or supplied or sidestreamed via line 8 throughdeep media filter 9 to anion-exchange unit 10, where the process isrepeated as described above. The portion to be diverted is controlled bypH controller 14 sensing tank 2 and controlling valve 15, using the sameprinciples used in FIG. 1. The other portion of the water from line 7 iscarried via line 11 to exit the system as end use or reuse or servicewater. Carbon dioxide can be added via line 12 as described above forFIG. 1 using pH controller 16 to control valve 17 to lower the pH asdesired or needed. Filter 9 removes particulate or fines (down to about1 micron particles) missed by or carried over from the clarifier. Anyfilter can be used; a backwash style is preferred.

A strong anion resin unit 10 (conventional bottle style) is installedconsisting of its associated equipment including a caustic storage tank(either sodium, potassium or ammonium hydroxide). The size of anion unit10 depends on the water quality, flow rate, contact time desired and howfilled it is with anion-exchange resin beads (preferably 20-40%). Carbondioxide can be provided via line 4 to the optional mixing tank 3 in theevent there is insufficient bicarbonate alkalinity in the water.

As can be seen, the unit of FIG. 2 is constructed and operated in mostrespects the same as or comparable to the unit as; of FIG. 1. The mixingtanks 2, 3 and clarifier 5 are the same as in FIG. 1; the operating pHsand conditions and controls are the same or comparable. When the filter9 and anion-exchange 16 unit 10 are filled with particulate, they arebackwashed as shown via backwash supply lines 18, 19 with the backwashbeing added to tank 2. As an option there can be a second filter 9and/or a second anion unit 10; the system can be switched to the backupswhile the first units are being backwashed and regenerated. After anionunit 10 is backwashed, it is regenerated by brining it with typically 4%NaOH, then slow rinsing, then fast rinsing, all as known in the art. Theslow and rapid rinse waters may be piped to a storage tank, where theymay be slowly pumped to tank 2; this is an optional step to reducereject fluid loading. optionally, anion unit 10 and filter 9 can bereplaced by a counter-current anion-exchange unit and counter-currentregeneration unit as in FIG. 1.

In both FIGS. 1 and 2 the spent regenerant from the anion resin iscollected in a storage tank 70 or 46 for off or on-site recovery; thesludge from the reactor/clarifier is also collected for off or on-siterecovery. With respect to regenerant recovery processes, ammoniumhydroxide can be used for anion regeneration and the spent regenerantcan be mixed with the produced sludge to create a nitrogen-richfertilizer. This fertilizer can be further augmented with phosphoruscompounds. Optionally, potassium hydroxide can be used as the anionregenerant. The spent potassium hydroxide regenerant can be a valuableproduct for use in wastewater plants (activated waste plant). Thepotassium would provide a valuable nutrient. to the process. Wheresodium hydroxide is used as the regenerant, the spent regenerant can beused as a reagent for aluminum processing, or a feed stock to caustic,soda ash or soda bicarbonate manufacture. If the water being treatedcontains high chlorides the spent regenerant can be used to manufacturesodium hypochlorite.

The sludge (sometimes referred to as lime sludge) produced can be(depending on the metals contained in the influent water) dried,pelletized and used in steel-making. Alternatively, the sludge (ifderived from water free of heavy metals) can be used in a utility powerstation flue gas desulfurization unit. If lime is used as theregenerant, gypsum or calcium chloride can be obtained as usefulby-products. The use of lime as a regenerant is desirable in waters witha high sulfate content or where there is a use for a gypsum slurry. Ifsodium or potassium hydroxide is used as the regenerant to treat highchloride waters the spent regenerant can be used as a feed stock to adiaphragm or membrane caustic plant to make the alkali and chlorine. Forwaters containing high sulfate where sodium or potassium hydroxide isused as regenerant, the spent regenerant is suitable as a feed stock toa LeBlanc Process (or comparable) soda ash, sodium bicarbonate orcaustic manufacturing plant.

Additional benefits of the invented system are as follows. Organics suchas oily materials that could normally foul an anion resin unit can beremoved in the flocculation process or by continuous counter-currentflow. Some portion of dissolved organic materials (primarily acids oranions) that would pass from a conventional lime softener are capturedin the invented process. The amount of reduction is a function of thepercent of flow through the anion circuit. Unlike Reverse Osmosis orevaporation technology, capital and operating costs are rather low.Maintenance is minimal and operating control is fairly simple. The unitcan handle a wide variety of influent waters and can automaticallyadjust to changes in influent quality.

As can be seen, the anion-exchange units in FIGS. 1 and 2 are usedindependently of any cation-exchange unit; there is no cation-exchangeunit (removing cations and adding H⁺) prior to the water going throughthe clarifier. It is noted that a small cation-exchange unit can beadded at the effluent end to polish the effluent water, such as toenhance the removal of sodium and/or lower the pH (Na⁺ being replaced byH⁺; H⁺ combining with OH⁻ to yield H₂O ), prior to the effluent beingsent out for use or service, but this is completely optional. Thisprocedure is particularly useful in waters with low magnesium andcalcium but high chloride content. Less preferably, where high sodiumwastewaters are being treated a magnesium cycle cation-exchange unit maybe placed in front of the anion train. (A magnesium cyclecation-exchange unit removes cations such as Na⁺ from the water andreplaces them with magnesium ions.) In this configuration sodium isremoved and is replaced by magnesium and the magnesium is then droppedout in its normal fashion in the invented process.

The following Examples further illustrate various aspects of theinvention.

EXAMPLE 1

A pilot plant was set up basically as shown in FIG. 1. Tanks 40-42 wereeach 30-gallon conebottom tanks; tank 20 was 30 gallons (pH about11.3-11.6) and line 32 was controlled via pH controller 25. Tank 21 (30gallons) was used and utilized CO₂ sparging via line 26 via a pHcontroller sensing tank 21 and maintaining pH at about 10.3-10.6.Clarifier 33 was a 70 gallon conebottom tank with overflow weir. Thetotal flow rate was 6 gallons/min. with 2 gal/min. through line 30 tounit 38 and 4 gal/min. through line 32 directly to tank 20. Each oftanks 40-42 was filled with about one cubic foot (about 40% of capacity)of Mitsubishi DIAION SA 20A anion-exchange resin beads which had beenprepared by soaking in 4% NaOH and rinsing in DI water. Total beadcontact time was thus about 18 minutes.

Resin beads were moved periodically from tank 42 to tank 41 to tank 40,particularly when the pH dropped in tank 20. Tanks 50-54 were 15 gallonseach; the rinse water in tank 54 came from tank 42 (pH 12.3-12.5). Theregenerant solution into tank 52 was 50% NaOH. The spent regenerantsolution from tank 50 (containing NaCl, Na₂SO₄, etc.) went to arecycling operation.

About 300 gallons each of five different source waters were run throughthe pilot plant. The results shown in Table 1 are the averages of threereadings. Calcium is expressed as CaCO₃; magnesium is expressed asCaCO₃; chloride is expressed as NaCl; sulfate is expressed as SO₄;sodium is expressed as Na.

TABLE 1 Influent Effluent Percent Source Water (ppm) (ppm) Reduction 1.wastewater 1 Calcium 1703 33 98.08% Magnesium 671 0.2 99.97% Chloride6800 2500 63.24% Sulfate 2160 417 80.69% Sodium 2860 2250 21.33% 2.wastewater 2 Calcium 1195 59 95.04% Magnesium 266 0.21 99.92% Chloride5000 3850 23.00% Sulfate 2175 1236 43.17% Sodium 2700 2360 12.59% 3.Cooling Tower water Calcium 745 51 93.15% Magnesium 1072 0.21 99.98%Chloride 4700 3000 36.17% Sulfate 7710 5220 32.30% Sodium 3690 321013.01% 4. well water 1 Calcium 723 17 97.64% Magnesium 290 6 97.99%Chloride 500 390 22.00% Sulfate 582 49 91.55% Sodium 332 268 19.28% 5.well water 2 Calcium 112 10 91.41% Magnesium 1065 0.21 99.98% Chloride150 50 66.67% Sulfate 68 0.3 99.56% Sodium 97 67 30.93%

The results, particularly the percent reductions, were surprising andunexpected.

EXAMPLE 2

Table 2 shows, for selected components, test results of water sampleNos. 6, 7 and 8 which were run through a static lab test configured orpatterned basically according to the design or configuration of FIG. 2,and run as per FIG. 2 described above. The resin beads were MitsubishiChemical DIAION SA 20A. The numbers are parts per million.

TABLE 2 Influent Effluent Influent Effluent Influent Effluent WaterWater Water Water Water Water Component No. 6 No. 6 No. 7 No. 7 No. 8No. 8 Calcium 462 28.9 26 25 30 24 (as Ca) Magnesium 240 0.147 6 0.1455.4 0.14 (as Mg) Chloride 2600 1700 715 600 1450 730 Sulfate 15000 100425 25 860 33 Silica 3.4 1.25 5 <1.0 7.6 <1.0 Sodium 2900 1740 Potassium81.8 48.2 Strontium 7.18 1.35 Lead 0.127 <0.01

These test results show that, to an extent that was surprising andunexpected, the process of the invention was effective in softening thewater and reducing the content of selected components. The inventionalso surprisingly lowered the sodium and potassium concentrations, asshown in water sample No. 6.

In addition to softening the influent water, the invention alsoeffectively reduces the concentration of undesirable anions(particularly chloride, sulfate, phosphate, nitrate and silicate) andreduces the concentration of undesirable amphoteric components andnon-hardness cations. It is believed, and testing thus far hasindicated, that the percent reductions shown in Table 3 can be achievedby the practice of the present invention; that is, the invention can beused to treat influent water having components (principally ionicmaterial) in the following concentration ranges (ppm) so as to achievethe percent reductions in concentration listed. For ppm concentrationcalculations, Ca and Mg are expressed as CaCO₃; Cl is expressed as NaCl;sulfate is expressed as SO₄; phosphate is expressed as P; nitrate isexpressed as NO₃; nitrite is expressed as NO₂; and silica is expressedas SiO₂. If there are two streams of water, the aggregate concentrationof a component in the two streams is the concentration which would existif the two streams were combined and mixed.

TABLE 3 Less Preferred Preferred Influent Influent Preferred LessPreferred Water Water Percent Percent Component ppm ppm ReductionReduction Ca 700-2000 100-5000 at least 98% at least 80, 90 or 95% Mg200-1000 100-4000 at least 99.9% at least 85, 90 or 95% Cl 500-2000100-7000 at least 95% at least 20, 40, 60, 80 or 90% Sulfate 500-2500100-20,000 at least 99% at least 25, 40, 60, 80, 90 or 95% Na or K300-1000 100-4000 at least 25% at least 10, 15 or 20% Cu, Pb, Fe,  1-10 0.5-40 at least 99% at least 70, Ba, Mn or 80, 85, 90, Sr 95 or 98% Zn,Cr, As,  1-10  0.5-40 at least 99% at least 50, Se, Ni, Ng, 70, 80, 90or Cd or Al 95% Phosphate  0.3-4  0.1-10 at least 99% at least 50, 70,80, 90 or 95% Nitrate  1-20  0.5-100 at least 99% at least 50, 70, 80,90 or 95% Nitrite or  1-30  0.5-100 at least 99% at least 50, Mo 70, 80,90 or 95% F  1-10  0.3-50 at least 99% at least 20, 40, 60, 80, 90 or95% Silica  1-30  0.5-150 at least 99% at least 50, 70, 80, 90 or 95%Cyanide  2-20  0.5-80 at least 95% at least 40, 60, 70, 80 or 90%

It is believed that Na and K are removed by association with Mg(OH)₂,magnesium silicate and CaCO₃ precipitates, such as by being entrained inthe molecular structure or being tied up or adsorbed onto the surface,etc. Silica is removed by precipitation as magnesium silicate and/oranion exchange removal. The anions are removed in the anion exchangeunit, by being entrained in the structure of other precipitates, bybeing adsorbed onto the surface of other precipitates, or in some casesby being removed as insoluble salt precipitates such as calciumphosphate or calcium sulfate or as complexes such as sodiumferrocyanide. With regard to the metal ions, some are amphoteric and areremoved in the anion-exchange unit, others go through the anion exchangeunit and precipitate out as their hydroxide or carbonate salt in thereactor/clarifier. The invented process and system will remove suchionic material as well or better than the traditional lime treatmentsystem. The traditional lime treatment system produces considerablesludge; the present invention avoids this by minimizing sludge and wasteproduction and eliminates many of the operational headaches ofconventional lime treatment.

The present invention can be used to produce drinking water in areas ofpoor quality and to convert seawater into drinking water; it can cleanor polish wastewater to create usable process water; it can polishprocess water for extended use. In areas with brackish water or highchloride or sulfate content, the invention can produce a rinse orprocess water that improves product quality in a process such as sodaash or sodium bicarbonate refining. In coastal areas it makes theproduction of magnesium hydroxide and magnesium oxide from seawater moreeconomical and environmentally friendly. Gypsum, magnesium hydroxide andcalcium carbonate may be individually formed. The effluent water fromsuch a process could be sent to a reverse osmosis (RO) process toproduce drinking water at a faction of the cost of normal RO processedseawater. With this process RO reject can be reintroduced into the headof the process to be reprocessed or evaporated to produce a mediumquality sodium chloride.

Anion content in the final effluent is greatly reduced. These anionswould include chloride, sulfate, nitrate, silicate, phosphate andorganic acids. The elimination of the organic component has the addedbenefit of color reduction and lowering of Total Organic Carbon (TOC).When the invention is applied in a drinking water application, thelowering of TOC will result in a lower potential of making THMs(Tri-HaloMethanes).

Although the preferred embodiments of the invention have been shown anddescribed, it should be understood that various modifications andchanges may be resorted to without departing from the scope of theinvention as disclosed and claimed herein.

What is claimed is:
 1. An anion-exachange system comprising ananion-exchange unit and a counter-current continuous resin regenerationunit, said anion-exchange unit utilizing anion-exchange resin and beingoperable to exchange anions in an aqueous stream, said counter-currentcontinuous resin regeneration unit being operable to receive usedanion-exchange resin from said anion-exchange unit, regenerate saidresin in a continuous counter-current manner, and return saidregenerated resin to said anion-exchange unit for refuse, said resinregeneration unit comprising a plurality of regeneration tanks includinga #1 regeneration tank and a #2 regeneration tank, said anion-exchangesystem further comprising a source of fresh regeneration solutionconnected by a first tube system to said #1 regeneration tank, said #1regeneration tank connected by a second tube system to said #2regeneration tank, said second tube system carrying effluentsubstantially free from anion-exchange resin from said #2 tank to said#1 tank, wherein said effluent carried from said #2 tank to said #1 tankoriginated as rinse water, said anion-exchange system further comprisinga source of rinse water connected by a tube system to one of saidplurality of regeneration tanks such that said rinse water flows oversaid anion-exchange resin and to said #1 regeneration tank, said sourceof rinse water being connected to a regeneration tank upstream of said#1 regeneration tank in the direction of regeneration flow.
 2. Ananion-exchange system according to claim 1, said resin regeneration unitcomprising at least a first regeneration tank and a second regenerationtank, said regeneration unit being operable to (a) receive usedanion-exchange resin in said first tank, said used anion-exchange resinhaving been used in said anion-exchange unit, (b) thereafter transferregenerant liquid from said second tank to said first tank, (c)thereafter transfer said resin from said first tank to said second tank,and (d) thereafter add regenerant liquid to said second tank, saidregenerant liquid transferred from said second tank to said first tankbeing more exhausted than said regenerant liquid added to said secondtank.
 3. An anion-exchange system according to claim 2, saidregeneration unit being further operable to (e) after step (b) removingregenerant liquid from said first tank, said regenerant liquid removedfrom said first tank being more exhausted than said regenerant liquidtransferred to said first tank from said second tank.
 4. Ananion-exchange system according to claim 1, wherein said anion-exchangeunit is a counter-current continuous anion-exchange resin train.
 5. Ananion-exchange system according to claim 4, wherein said counter-currentcontinuous anion-exchange resin train comprises at least two separatetanks.
 6. An anion-exchange system according to claim 5, wherein eachtank of said anion-exchange resin train is filled to 20% to 40% ofcapacity with anion-exchange resin in bead form.
 7. An anion-exchangesystem according to claim 4, wherein said counter-current continuousanion-exchange resin train comprises at least three separate tanks. 8.An anion-exchange system according to claim 1, wherein saidcounter-current continuous resin regeneration unit comprises at leastfive tanks.
 9. An anion-exchange system according to claim 1, whereinsaid anion-exchange unit is adapted to release hydroxyl ions.
 10. Ananion-exchange system according to claim 1, said system being operableto provide effluent from said anion-exchange unit as influent rinsewater in said resin regeneration unit.
 11. An anion-exchange systemaccording to claim 1, said system being operable to provide effluentfrom said anion-exchange unit having a pH of at least 9.5.
 12. Ananion-exchange system according to claim 1, said system being operableto provide effluent from said anion-exchange unit having a pH of atleast 10.6.
 13. An anion-exchange system according to claim 1, saidsystem being operable to provide effluent from said anion-exchange unithaving a pH of at least 11.3.
 14. An anion-exchange system according toclaim 1, said system being operable to provide effluent from saidanion-exchange unit having a pH of at least
 12. 15. An anion-exchangesystem according to claim 1, wherein said fresh regenerant solution isNaOH solution.
 16. An anion-exchange system according to claim 1,wherein said rinse water is provided as effluent from saidanion-exchange unit.
 17. An anion-exchange system according to claim 1,wherein said anion-exchange unit is adapted to treat about 33% ofinfluent water coming into said anion-exchange system at a flow rate of50-1000 gallons per minute.